34 BRITISH DESMIDIACE^E. 



Cells very small, subquadrate, about as long as 

 broad, deeply constricted, with a linear sinus ; semicells 

 transversely rectangular with straight sides and apex, 

 basal and apical angles scarcely rounded, apical angles 

 sometimes very slightly produced ; cell- wall uniformly 

 granulate giving the margins a minutely crenulate 

 appearance, granules disposed in transverse rows, three 

 of which are visible across the front of each semicell. 

 Side view of semicell circular. Vertical view elliptic, 

 ratio of axes about 1 : lv. 



Zygospore unknown. 



Length 1 6-17*5 /z; breadth 17-18'5/x; breadth of 

 isthmus 6*5-7 /x; thickness 10 fji. 



ENGLAND. Mickle Fell, N. Yorks ! 



SCOTLAND. Ben Chiurn, Perth ! 



241. Cosmarium promontorium W. & G. S. West. 



(PI. XCIV, fig. 9.) 



Cosmarium promontorium W. & G. S. West, New Brit. Freshw. Alg-. 1894, 

 p. 7, t. 1, f . 14 ; Nordst. Index Desmid. 1896, p. 206. 



Cells small, about 1^ times longer than broad, deeply 

 constricted, sinus narrowly linear with a dilated 

 extremity ; semicells broadly subrectangular, with the 

 sides more or less irregularly biundulate, with three 

 crests (including the basal and apical angles) and two 

 hollows, the upper hollow being deeper than the lower 

 one, basal angles rounded, apical angles subacute and 

 prominent, apex convex but widely truncate in the 

 middle ; with one series of minute granules just within 

 the margin of each semicell, about four within each 

 lateral margin and four within the apex. Side view of 

 semicell rounded-ovate, with the upper part of the 

 sides slightly retuse. Vertical view elliptic, with a 

 small inflation at the middle 011 each side. Chloroplasts 

 axile, with one pyrenoid in each semicell. 



Zygospore unknown. 



Length 22 p.; breadth 17/i; breadth of isthmus 

 3'5/x; thickness 10'5/*. 



IRELAND. Oorid Lough, Galway ! 



